Criminal? He turned out to be above board (5-3-7)
I believe the answer is:
under-the-counter
'criminal?' is the definition.
(thesaurus)
'he turned out to be above board' is the wordplay.
'out' indicates an anagram (out can mean wrong or inaccurate).
'to be above' says to put letters next to each other (in a down clue, some letters go above others).
'board' becomes 'counter' (**).
'turned' anagrammed gives 'undert'.
'he' after 'undert' is 'underthe'.
'underthe'+'counter'='UNDER-THE-COUNTER'
(Other definitions for under-the-counter that I've seen before include "Hidden from customers' sight" , "Illicit" , "Possible location of panic button" , "illegal" , "Sold illegally or secretly" .)